Trailing arm suspensions with mechanically linked and actuated height control valves are well known. FIG. 1 illustrates such a trailing arm suspension 10 in combination with a height control valve 12. The trailing arm suspension 10 comprises opposing trailing arm assemblies 11 mounted on opposite sides of the vehicle, preferably to the vehicle frame rails 16. Each of the trailing arm assemblies includes a trailing arm 14 having one end pivotally connected to a hanger bracket 18 by a pivotal connection 20. The hanger bracket is suspended from the vehicle frame rail 16. The other end of the trailing arm 14 mounts to an air spring 22, which is affixed to the frame rail 16. The air spring 22 dampens the pivotal rotation of the trailing arm 14 about the hanger bracket 18 relative to the frame rail 16.
An axle assembly 28 typically spans and mounts to, or is carried by, the trailing arms 14. The axle assembly 28 rotatably mounts ground-engaging wheels (not shown). Any movement of the wheels in response to their contact with the ground will result in a rotation of the trailing arms 14, which is resisted by the air springs 22.
The air springs 22 typically comprise an air bag 24 and a piston 26. The piston 26 is mounted to the trailing arm 14 and the air bag 24 connects the piston to the frame. Pressurized fluid can be introduced or exhausted to adjust the dampening performance of the air spring. Additionally, the volume of air in the air spring can be adjusted to alter the height of the frame rails relative to the trailing arms. Often, there is a preferred or reference ride height for the trailer and, depending on the load carried by the trailer or the operating environment, the actual or current ride height can vary over time. Pressurized air is introduced to or exhausted from the air bags to adjust the relative height of the trailer frame rail with respect to the trailing arms to maintain the ride height at the reference height for a particular load or environmental condition.
The adjustment of the ride height is accomplished by the height control valve 13, which has an inlet port, an operation port, and an exhaust port. The inlet port is fluidly connected to a source of pressurized air for the vehicle. The operation port is fluidly connected to the air bags 24 of the air springs and, the exhaust port is fluidly connected to the atmosphere. The height control valve controls the fluid connection of the operation port with the inlet port and the exhaust port to introduce or exhaust air from the air spring to thereby adjust the vehicle height.
The height control valve is typically mounted to the vehicle frame 16 and has a rotatable lever arm 32 that is operably connected to the trailing arm 14 through an adjustable rod 34, whereby any movement of the trailing arm 14 results into a corresponding movement of the lever arm to move the valve and connect the operation port to either of the inlet port or exhaust.
A traditional height control valve has three positions: an inflate position, a neutral position, and an exhaust position in the inflate position, the lever arm 32 is rotated up and the operation port is connected to the inlet port. In the neutral position, 20 the lever arm 32 is generally horizontal and the operation port is not connected to either the inlet or exhaust ports. In the exhaust position, the lever arm is rotated down and the operation port is connected to the exhaust port.
The various height control valves currently available can be operated on a time delay or can respond instantly to changes in height. The valve structure for these valves typically includes multiple spring biased pistons or similar elements that seal the various ports in response to the relative movement of the trailing arm. Examples of this type of height control valve are disclosed in U.S. Pat. No. 5,161,579, issued Nov. 10, 1992; U.S. Pat. No. 5,560,591, issued Oct. 1, 1996; and U.S. Pat. No. 5,375,819, issued Dec. 27, 1994.
These valves tend to use a seal in the form of an O-ring or the like that surround the dynamic or moving piston to seal the piston relative to the valve housing. These “dynamic” seals are subject to wear as the piston reciprocates, leading to their eventual failure.
Other suitable valves include valves without any dynamic seals. A group of these valves are referred to as shear valves and comprise abutting plates, one of which is movable relative to the other. The plates are retained together by the pressurized air from the vehicle air system, negating the need for any dynamic seals such as is disclosed in PCT/US00/23278, which is incorporated by reference.
The most commonly used current height control valves, regardless of their valve structure, are subject to damage because of the mechanical coupling between the trailing arm and the height control valve. The mechanical coupling is directly exposed to the environment of the trailing arm suspension, which can be very harsh. Additionally, most of the mechanically operated valves are susceptible to “freezing” if not used regularly.
In response to the disadvantages of the mechanically actuated and controlled height control valves, electronically controlled and actuated height control systems have been developed. The electrical-based systems form a small segment of the height control valve market. These electronically controlled systems typically use various sensors to monitor the vehicle height position and use electrically actuated valves, such as solenoid valves, to control the introduction and exhaustion of air from the air springs. A disadvantage of the electronically controlled systems is that they are more costly that the mechanical systems in component cost, maintenance cost, and operation cost. However, they are beneficial in that they tend to be more responsive to changes in the vehicle height.
Thus, there is still a need in the vehicle height control system to have a height control system with the low cost of the traditional mechanical systems in combination with the performance of the electronic systems.